Injection moulding machine with integrated hot channel system

ABSTRACT

An injection moulding machine for producing small plastic components with a drive unit ( 6, 84 ), a plasticizing device ( 4, 42 ) and a hot channel nozzle ( 1 ) having a collection chamber ( 10 ) for the molten plastic. An injection ram ( 35 ) projects into the hot channel nozzle ( 1 ) and can push the collected plastic out. In an embodiment, the plasticizing device ( 4, 42 ) and the drive unit ( 6, 84 ) are secured to a movable bearing housing ( 85 ) and can move the injection ram ( 35 ).

FIELD OF THE INVENTION

The present invention relates to an injection moulding machine forinjection moulding of plastic miniature parts.

BACKGROUND OF THE INVENTION

Such injection moulding machines are generally known and basicallycomprise an injection aggregate and a closure arrangement for the formtools, whereby the injection aggregate has an extruder for plasticizingthe synthetic material and a collection chamber for the plasticizedmass, which is either ejected by an axial movement of the extrusionscrew or by a separate injection ram out of the injection nozzle of theextruder. The form tools with their cavities are clamped between twoclamping plates of the closure unit, whereby the injection nozzle of theextruder, during ejection of the plasticized mass, tightly contacts thedie plate of the injection moulding machine by pressure of force.

In these machines, the melted material is pressed from the collectionchamber of the extruder over feed or sprue channels arranged in a hotchannel distributor into the cavities and, as a rule, molten materialfor a number of injection cycles is in the feed path between thecollection chamber and the cavity. This material is subjected torepeated, abrupt compressions and accompanying temperature fluctuationsover a period of time, and therefore, by the time it is filled into thecavities, the material already exhibits a reduction in quality or evenparticles of decomposition products. It is understood that products madewith such material may exhibit faults or early fatigue symptoms.

A further and to date unsolved problem in the production of small partsis to be seen in the large quantity of sprue pieces occurring.Conventionally produced small parts always have a sprue piece, theweight of which can be well in excess of that of the part beingproduced, and which must be removed in a separate work step.

In this way, production with needle-free nozzle-closure devices canresult in approx. 95% of the injected material being waste material andusable parts being produced from a mere 5% of the injected material.Even if this waste material is recycled into the plasticizing process,the characteristic properties of the respective plastics suffer and theminiature parts produced with this material no longer are able tocompletely meet the requirements expected from them.

In order to reduce the problem associated with hot channel distributors,DE-A-42'39'776 suggests providing an injection moulding machine for thesimultaneous production of two miniature plastic parts, in which theinjection arrangement is provided with two injection aggregates. In sucha device, the plasticizing, the injection process and the post-pressurecontrol are individually carried out for each miniature part to beproduced, in order to reach the quality required for these parts withminimal production losses. In the production of high quality miniatureparts it has proven particularly difficult to manufacture a number offorms simultaneously and within the required low permissible deviation,i.e. without intrinsic tension or production error and with precisefilling weight.

It is therefore the object of the present invention to provide aninjection moulding machine for producing qualitatively impeccable, wearresistant and durable parts, preferably miniature parts made oftechnical plastics, such parts being produced with as little waste aspossible.

An arrangement described in the publication “Plastiques Modernes etElastomères”, Vol. 35, Nr. 1, January/February 1983, Paris, France, Page41, has a distribution block, which—in contrast to conventionalinjection moulding machines—is fixedly connected to the machine part.This distribution block bears on its front side, i.e. towards the formdies of the injection die a plurality of fixedly mounted injectionnozzles which protrude into the first form plate of the injectionmoulding die. When filling the form cavities, these nozzles, which arefixedly connected to the distribution block and are hot, are broughtinto contact with the closed and cold injection moulding die via aplurality of infeed channels. After filling the form cavities, the colddie is separated from the hot distribution block and its nozzles. Inthis way the individual nozzles can again be brought up to the requiredhigh temperature, whilst the injection moulded parts can remain in theclosed die in order to continue cooling, prior to opening the die forremoving the injection moulded parts. The collection chamber of thisassembly is located in the machine part, which has proven to bedisadvantageous for the production of miniature parts because of thelength of the injection channels. At this point it should be stressedthat when producing miniature parts, a long retention time of the meltin the hot infeed channels leads to material decomposition.

It is therefore the object of the present invention to provide aninjection moulding machine for producing qualitatively impeccable, wearresistant and durable parts, preferably miniature parts made oftechnical plastics, such parts being produced with as little waste aspossible.

Miniature parts such as can be manufactured with the injection mouldingmachine according to the present invention, normally have a weight ofbetween 0.001 grammes to 5 grammes. However, it is to be understood thatparts with a weight of up to 50 grammes or more can be produced.

SUMMARY OF THE INVENTION

This task is inventively solved with an injection moulding machine withthe characteristics of claim 1, and in particular with a machine inwhich the retention time of the plasticized, compressed hot plasticsmaterial in the collection chamber (also called piston tab or screw tab)is lowered by a shortening of the injection path of the melt. Inparticular, this shortening of the injection path is achieved byarranging the collection chamber immediately behind the outlet port ofthe nozzle tip.

In a first embodiment of the invention, the melt which is produced in aplasticizing cylinder is transported over a hot channel adapter into anozzle body and is collected in a collection chamber within the nozzlebody. The ready melt in this collection chamber is ejected with the aidof a piston and is pressed via injection channels into the cavities. Inthis embodiment, the ejection piston has an axial core (piston internalfeed channel) having a lateral inlet port through which the melt is fedinto the collection chamber, and also a ball valve at its tip, whichcloses off the collection chamber during ejection. The outlet port ofthe injection channels are closed or opened by means of a needle closuredevice.

In another embodiment of the invention, the melt is produced directlybehind the hollow cylinder type ejection plug and is transported axiallythrough this hollow cylindrical plug into the collection chamber (plugtab). Again, the collection chamber in the nozzle body can be closed offtowards the feed or transportation channel of the hollow cylindricalplug, and the outlet ports of the nozzle tip can be sealed of with aneedle shut-off device.

In a further embodiment of the invention, the melt is not fed throughthe piston itself, but is directly fed into the collection chamber. Asliding arrangement which is coupled to the needle closure device allowsthe collection chamber to be automatically closed off from the feedchannel.

The advantages of the inventive injection moulding machine areimmediately obvious for the man skilled in the art. Thus, the shorteningof the injection path permits a more controlled increase in pressure inthe cavity and enables an exactly dosed filling of the cavity with hotmelt, which leads to injection moulded parts with little productiontolerance (deviation from permissible value). Of course, with such amachine the cavities can be filled rapidly requiring only a low machinefilling pressure. Energy savings and little wear and tear are furtheradvantages of this shortened injection path.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention shall be more closely described with theaid of an embodiment and the Figures, in which

FIG. 1 shows a schematic view of a first embodiment of an inventiveinjection moulding machine in cross section;

FIG. 2 shows a schematic view of the accompanying hot channel nozzle incross section;

FIG. 3 shows a schematic view of a constructional variation of thisinjection moulding machine in cross section;

FIG. 4 shows a schematic view of a further embodiment of the inventiveinjection moulding machine in cross section;

FIG. 5 shows a detailed view of this further embodiment of the inventiveinjection moulding machine in cross section;

FIG. 6 shows a detailed view of the hot channel nozzle of the embodimentaccording to FIGS. 4 and 5 in a filled state; and

FIG. 7 shows a detailed view of the hot channel nozzle of the embodimentaccording to FIGS. 4 and 5 in an emptied state.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The injection moulding machine shown in FIG. 1 comprises a drive unit 6,a plasticizing device 4, in particular a plasticizing cylinder, a hotchannel adapter 2, a piston and needle closure drive 3, as well as aninventive hot channel nozzle 1 as the basic assemblies. In operation,the plastic granules to be processed are fed from the granule container53 through the granule feed channel 54 into the cylinder tube 41. Theplasticizing screw 42 lying in the cylinder tube 41 is driven by a drivemotor 61 via a screw coupling 65. The cylinder tube 41 is heated bymeans of known ring heating elements 46 and is mounted on an adapter 43at its outlet side. This adapter 43, in combination with a clip 66,ensures a pressure-tight connection to the hot channel adapter 2,through which the plasticized material is fed into a collection chamber10. According to the invention, this collection chamber 10 lies in thehot channel nozzle 1. The material collected in the collection chamber10 can be directly pressed into the cavities of the forming tool throughthe nozzle tip 12 of the hot channel nozzle 1. The injection ram 35 iscarried in a guiding and wear insert 19 and, in the embodiment shown,has a central bore whose end towards the drive has an inlet opening andwhose outlet opening at the end towards the tool has a back-pressurevalve, for example a ball valve. According to the invention, theinjection ram 35 protrudes into the nozzle body 11 of the hot channelnozzle 1, which nozzle is heated with the aid of nozzle heating elements13 and which ram bears a nozzle tip 12. This nozzle tip 12 has one ormore injection channels with outlet openings which lead to the inletopenings of the individual cavities. In the shown and preferredembodiment, these outlet openings are axially displaced to the injectionram 35 in order to be able to guide the closure needles 15 outside ofthe guiding insert of the injection ram 35.

In a first operational phase the plasticized material, and in particulartechnical plastics such as PET, ABS, PIC or similar, to fed through thematerial feed channel 24 of the hot channel adapter 2 in to the inletopening of the injection ram bore and further on through the openedback-pressure valve 36 into the collection chamber 10 and the injectionchannels, whose injection openings are closed by means of the closureneedles 15. In this way, as much material is provided as is necessaryfor filling the respective cavities.

In a second phase the closure needles 15 are withdrawn in order torelease the injection openings; then the required pressure is built upby means of the injection ram 35 in order to press the material combinedin the collection chamber 10 into the cavities of the die plates 17.According to the invention, the correct pressure for uniformdistribution and precise filling of the material is built up directly inthe cavities. Due to the forward motion of the injection ram 35 theback-pressure valve is closed and the prescribed quantity of material ispressed into the cavities. After filling is completed the injectionopenings are closed by means of the closure needles 15. The retreatingmovement of the injection ram 35 automatically causes the back-pressurevalve to be relieved and, due to the feed pressure of freshlyplasticized mass, to be reopened. The control of the individualcomponents is within the scope of the person skilled in the art and isnot subject of the present invention.

FIG. 2 shows the inventive hot channel nozzle 1 in detail. Thiscomprises a nozzle body 11 with a collection chamber 10 arrangedtherein. By means of heating elements 13 this nozzle body 11 can bebrought up to or stabilized at the temperature required for processing.In a preferred embodiment, the nozzle body 11 has a length of approx.120 mm and a diameter of approx. 35 mm. The collection chamber 10 has adiameter of approx. 10 mm. Preferably the nozzle body 11 is made of onesingle piece, but can have a separate nozzle tip 12 being made of adifferent material. In the present embodiment there are four injectionchannels 14 which can be closed or opened by means of needles 15 of theneedle closure device. According to the invention, the nozzle tip of thehot channel nozzle 1 protrudes through the machine side die plate 17′and pressure-tightly abuts the cavity-forming die plate surface.

The injection ram is hollow on the side facing the cavities and on theside facing the machine it has a lateral inlet opening, over which theplasticized plastic melt can be transported from the plasticizing deviceinto the collection chamber 10. A back-pressure valve 36 prevents theplastic melt from flowing back out of the collection chamber 10 into thebore 24 of the injection ram 35 during its forward movement. A guidingand wear sleeve (19) supports the leakage-free pressing of the plasticmass out of the collection chamber 10. In order to be able to melt andtransport plastic material also during the pressing-out phase, theguiding and wear sleeve 19 has a free groove 18, over which the machineside inlet opening of the injection ram's central bore remains connectedto the material feed channel 24.

It is to be understood that the construction of the inventive injectionmoulding machine can be adapted to known plasticizing devices andpressure-generating pressing means. FIG. 3 shows a further embodiment,in which the material feed channel 24 is directly connected to theinjection channel side end of the collection chamber 10. In thisconstructional variation, an injection ram with back-pressure valve isnot required and the collection chamber 10 can be directly closed offfrom the material feed channel 24 by means of a slide coupled to theneedle closure device. Preferably, instead of employing passive valvesystems, actively operatable, i.e. controllable closure means can beused, thereby allowing for an even more precise dosing of the plasticmass to be injected.

In the embodiment as shown in FIG. 4, the plasticizing device and thepressure-generating means for ejecting the plastic material resting inthe collection chamber 10 are arranged axially behind each other. Theconstruction of the inventive hot channel nozzle 1 essentiallycorresponds to that as shown in FIG. 2. However, the ram 35 in thisembodiment is guided axially through the plasticizing screw 42.

In the embodiment as shown in FIG. 5, the plasticizing screw 42 and thehot channel nozzle 1 lie axially behind each other. For this purpose,the injection ram 35 is provided with a material feed channel 24, and inparticular a central bore. The screw 42 is guided in a heatablecylindrical tube 82 and is provided with the required plastic materialout of a granule hopper 83. This plasticizing screw 42 is driven by adrive motor 84 and is attached to a supporting frame 85 together withthe cylindrical tube 82. This supporting frame 85 has a guiding carriage86 which is slidingly supported on a guiding rail 87. By means of apneumatic drive 88 the supporting frame 85 can be displaced on thisguide rail 87 together with the drive motor 84, the cylindrical tube 82and the injection ram 35. When the collection chamber 10 is being filledwith plasticized synthetic material the supporting frame 85 is pushedback on the guide rail 87 together with the plasticizing screw 42 andthe drive motor 84. In order to empty the filled collection chamber 10,closure needles 15 are withdrawn and the pneumatic drive 88 isactivated. Typically, the collection chamber has a diameter of 6-12 mmand a length of 100-150 mm. In the present embodiment the needle closureplate 89 for activating the needles is arranged directly behind the hotchannel nozzle 1 and needles having a length of 100-120 mm can be used.

FIG. 6 shows the nozzle body and the guiding mechanism of the closureneedles in detail. The nozzle body 11 is rigidly fixed in the fixedforming plate 16 and on the sprue side protrudes into the die mould 17.This nozzle body 11 can comprise one or more injection channels 14 whichcan be closed with closure needles 15. These closure needles 15 arecollectively attached to a closure needle plate 89 which can bedisplaced over a piston-pressure-system. 90. During the plasticizingstep the plastic flows into the injection channels 14 and to thecollection chamber 10. Thereby the injection ram 35 is pressed outwardstogether with the cylindrical tube 82, the plasticizing screw 42 and thedrive motor 84.

As shown in FIG. 7, in order to fill the die cavities the needle closureplate 89 is pushed backwards with the aid of the piston-pressure-system90, and thereby withdrawing the closure needles 15 from the openings ofthe nozzle tip 12. At the same time the injection ram 35 is pushed intothe collection chamber 10, together with the plasticizing screw 42 beingattached in the supporting frame 85. A back-pressure valve 36, and inparticular a ball valve, closes the central bore 24 of the injection ram35, thereby permitting an exactly dosed filling of the die cavities.

By means of the present invention, machine hot channel distributors areno longer required and the total retention time in the injectionchannels of the plastic mass which is heated up to approx. 500° C. canbe reduced to two cycles. Additionally, the design of the individualtools is extremely simplified because, for example, hot channels andneedle closure are no longer required.

It is to be understood that the embodiments herein described only serveto illustrate the invention and can be modified by the expert withoutrequiring a further inventive step. Thus, instead of the piston, a screwwith injection head, or instead of the back-pressure valve an adjustableor automatic pressure valve can be installed. Also, for closure of thenozzle tip channels a gate or other types of valves can be used. Theinclusion of ventilation channels and specific seals, as well astemperature regulation and control of the individual machine parts isalso within the scope of the common knowledge of the expert. It is alsobe to understood that the injection moulding machine can be dimensionedso as to be suitable for producing larger parts.

What is claimed is:
 1. Injection moulding machine for injection mouldingof plastic parts, with a plasticizing device for plasticizing plasticgranules, having a collection chamber for plastic material plasticizedin the plasticizing device, having a material infeed channel between theplasticizing device and the collection chamber, and having an injectionram for ejecting plastic material collected in the collection chamber,characterized in that the injection moulding machine comprises a hotchannel nozzle having at least one injection channel and that thecollection chamber lies within this hot channel nozzle, said hot channelnozzle protruding through a die plate.
 2. Injection moulding machineaccording to claim 1, characterized in that the hot channel nozzlecomprises a nozzle body and a removable nozzle tip.
 3. Injection moldingmachine according to claim 1, characterized in that the injection ramcomprises a bore having a drive oriented end and a machine oriented end,wherein said drive oriented end has at least one lateral inlet openingand said machine oriented end has a back-pressure valve.
 4. Injectionmolding machine according to claim 3, characterized in that theback-pressure valve is a ball valve.
 5. Injection molding machineaccording to claim 3, characterized in that the injection ram is in aguiding and wear sleeve.
 6. Injection moulding machine according toclaim 1, characterized in that for closure of the at least one injectionchannel a needle closure device is provided.
 7. Injection moldingmachine for injection moulding of plastic parts, with a plasticizingdevice for plasticizing plastic granules, having a collection chamberfor plastic material plasticized in the plasticizing device, having amaterial infeed channel between the plasticizing device and thecollection chamber, and having an injection ram for ejecting plasticmaterial collected in the collection chamber, characterized in that theinjection moulding machine comprises a hot channel nozzle having atleast one injection channel and that the collection chamber lies withinthis hot channel nozzle, said hot channel nozzle protruding through adie plate, and wherein the material infeed channel opens into a regionof the collection chamber adjacent thereto.
 8. Injection molding machinefor injection moulding of plastic parts, with a plasticizing device forplasticizing plastic granules, having a collection chamber for plasticmaterial plasticized in the plasticizing device, having a materialinfeed channel between the plasticizing device and the collectionchamber, and having an injection ram for ejecting plastic materialcollected in the collection chamber, characterized in that the injectionmoulding machine comprises a hot channel nozzle having at least oneinjection channel and that the collection chamber lies within this hotchannel nozzle, said hot channel nozzle protruding through a die plate,and wherein an end of the material infeed channel adjacent to thecollection chamber is provided with a controlled closure device. 9.Injection molding machine according to claim 6, characterized in thatthe needle closure device is provided with a pressure piston device. 10.Injection molding machine according to claim 9, characterized in thatthe needle closure device is arranged between the hot channel nozzle andthe plasticizing device.